Electromagnetically actuated valve for hydraulic motor vehicle brake systems

ABSTRACT

The valve has a seat valve with a hollow-conical valve seat and a closing member in the form of a spherical layer on a longitudinally drilled tappet. An inflow bore communicating with a pressure medium inlet discharges centrally into the valve seat. The largely pressure-equalized tappet is engaged by a magnet armature acting on the seat valve in a closing manner and by a restoring spring acting in the opening direction. The valve embodied in principle as a switching valve is controllable into stable intermediate positions on the basis of the following provisions: the cone angle of the valve seat is at most 90°; the force at the closing member, originating in the restoring spring, is adapted such that it has a course that decreases monotonously with an increasing valve opening stroke (h); the magnet circuit of the valve is embodied such that the magnetic force (F M ) exerted on the magnet armature and transmitted to the closing member is variable in infinitely graduated fashion and has a course that decreases monotonously with increasing valve opening stroke (h), the negative slope of which course is less quantitatively than that of the course of spring force.

PRIOR ART

The invention is based on an electromagnetically actuated valve forhydraulic motor vehicle brake systems.

In slip-controlled hydraulic brake systems, valves are used which intheir electromagnet-actuated closing position are subjected to verystrong hydraulic opening forces. The electromagnetic circuit of thesevalves must therefore, in the valve closing position, bring to bear aholding-closed force on the magnet armature that is greater than themaximum hydraulic opening force plus the force of a restoring spring. Amagnetic circuit designed in this way requires corresponding space forinstallation and with other disadvantages prevents the disposition ofsuch valves in a space-saving, tight package.

German Patent Application DE 31 26 246 A1 discloses a valve of thisgeneric type in which to reduce the holding-closed force by means ofpressure equilibrium operative at the tappet, a relatively short pin inthe end portion toward the valve dome of the tappet that is passedthrough the magnet armature and form-lockingly united with it isdisposed, such that it is movable for steering purposes, in alongitudinal bore of the tappet. A force originating in the inflow-sidepressure on the pin is therefore deviated via the valve dome to thevalve housing. This provision allows making the magnet circuit smallerin size. Functionally, the known valve is a 2/2-way valve, which hasonly two switching positions, in which the full flow cross section of aseat valve is either uncovered or fully blocked. This lessens themobility of such valves. Moreover, their considerable switching noisesare often disadvantageous.

ADVANTAGES OF THE INVENTION

The valve according to the invention has the advantage over the priorart that in a way similar to a proportional valve, it can betransferred, by controlling the magnetic force and with short strokes,to an arbitrary number of intermediate positions but without having tohave the complicated design of a proportional valve. This mode ofoperation can be ascribed to the fact that the restoring springessentially determines the course of the force engaging the tappet overthe valve stroke, while the hydraulic force acting on the closing memberhas only subordinate influence, because of the diameter ratios of theinflow bore and the sealing diameter of the valve seat and because ofthe force deviation to the valve dome. A largely continuous flow controlis therefore attainable with the valve of the invention. In manyapplications it can be used instead of proportional valves. Inslip-controlled brake systems, the use of the valve of the inventionmakes it possible to achieve a higher closed-loop control quality andlower noise emissions than in the known valve.

By means of the provisions recited in the dependent claims, advantageousrefinements of and improvements to the valve defined by claim 1 arepossible.

With the embodiments defined herein a more-defined separation of thestream of pressure medium from the closing member or the valve seat isattained after the valve opens. Unstable flow forces are thus largelyavoided.

The refinement of the invention defined has the advantage that a streamof pressure medium once separated from the closing member and the valveseat, in its further course now no longer strikes the tappet. Thisprecludes disruptive influences of flow forces.

With the embodiment of the invention defined hereinafter, it is possiblein a simple way to adjust the spring force of the restoring spring, forinstance in the closing position of the seat valve, by adjusting theposition of the sleeve relative to the tappet.

BRIEF DESCRIPTION OF THE DRAWINGS

One exemplary drawing of the invention is shown in simplified form anddescribed in further detail in the ensuing description.

FIG. 1 shows a longitudinal section through an electromagneticallyactuated valve with a seat valve;

FIG. 2 shows a detail II of FIG. 1 in the form of the seat valve, in theclosing position, on a larger scale than in FIG. 1; and

FIG. 3 shows a graph of the forces operative in the seat valve over thevalve opening stroke.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

An electromagnetically actuated valve 10 shown in FIG. 1 of the drawinghas a valve housing 11, with which it is received in a valve block 12.Outside the valve block 12, the valve housing 11 is continued in a polecore 13. An annular magnet coil 16, enveloped by a housing 15 thatconducts magnetic flux, is slipped onto both the valve dome and the polecore 13.

A longitudinally movable magnet armature 19 is located in the valve dome14. It engages a tappet 20, onto which a sleeve 21 is press-fitted. Thetappet 20 and the sleeve 21 are longitudinally movably received in alongitudinal bore 22 in the pole core 13 and the valve housing 11. Arestoring spring 23 engages a face-end support face 24, remote from thearmature, of the sleeve 21 (FIG. 2).

The restoring spring 23 is supported on a valve body 25 that ispress-fitted into the valve housing 11 and drilled throughlongitudinally. The valve body communicates with a pressure medium inlet26 of the valve 10, which in turn communicates with a line bore 27 ofthe valve block 12.

The valve body 25, toward the tappet, has a hollow-conical valve seat 28with a cone angle α of at most 90° (FIG. 2). An inflow bore 29 with thediameter D₁ and communicating with the pressure medium inlet 26discharges centrally into the valve seat 28. The valve seat 28 endsradially outward in a sharp edge at a support face 30, which demarcatesthe valve body 25 with respect to a valve chamber 31 and extends atright angles to an axis in which the valve body 25, the valve seat 28,the tappet 20 and sleeve 21, and the magnet armature 19 are located.

The valve chamber 31 communicates with a transverse bore 32, which formsthe pressure medium outlet 33 of the valve 10 and communicates with aline bore 34 of the valve block 12. The longitudinal bore 22 and thevalve dome 14 communicate in a pressure-fluid-carrying way with thevalve chamber 31. The magnet armature 19 and the tappet 20 with thesleeve 21 are therefore bathed by a pressure medium.

A closing member 37 in the form of a spherical layer cooperates with thevalve seat 28. The closing member 37 is embodied on its face end on areduced-diameter cylindrical portion 38 of the tappet 20 in the valvechamber 31. The cone angle α of the valve seat 28 and the radius R ofthe closing member 37 are adapted to one another in such a way that thesealing diameter D₂ of the valve seat is equivalent to or slightlylarger than the diameter D₁ of the inflow bore 29. The diameter D3 ofthe tappet portion 38, by comparison, is at least approximatelyequivalent to the sealing diameter D₂ of the valve seat 28; that is, thetappet portion 38 is slightly larger than the sealing diameter. Thetransition of the closing member 37 to the tappet portion 38 is embodiedin sharp-edged fashion. The tappet portion 38, including the closingmember 37, has an axial length L that is equivalent at least to thesealing diameter D₂ of the valve seat 28. The tappet portion 38, after atransitional portion 39 with the valve seat 28 of correspondingconicity, changes over into the tappet 20. It can also be seen in FIG. 2that the termination of the valve seat 28 in the end face 30 has adiameter D₄ that is at least twice the sealing diameter D₂ of the valveseat.

In the common axis of the magnet armature 19, tappet 20 and valve body25, a longitudinal bore 42 that penetrates the tappet over its entirelength originates at the closing member 37. Toward the valve body, thelongitudinal bore 42 initially has an axially short first bore portion43, whose diameter is equal to the diameter D₁ of the inflow bore 29 ofthe valve body 25 (FIG. 2). Toward the magnet armature 19, the firstbore portion 43 merges with a second portion 44 of the longitudinal bore42. This second portion has a reduced diameter D₅ compared with thefirst bore portion 43. Following the portion 44, the longitudinal bore42 is continued in the form of a third bore portion 45, toward thearmature, and the diameter D₆ (FIG. 1) of this portion is larger thanthe diameter D₅ but smaller than or equal to the diameter D₁ of theinflow bore 29. A first pin 46 is longitudinally movably received in thebore portion 45. The pin 46 extends in one direction to near the secondbore portion 44 and on the other as far as the magnet armature 19. Bymeans of very close tolerances and a high surface quality of the boreportion 45 in the pin 46, there is only very slight play between the twocomponents. The fit between the pin 46 and the bore portion 45 cantherefore be considered as low-leakage and therefore largelypressure-tight. Moreover, the pin 46 is of a material that has a highercoefficient of temperature expansion than the tappet material. In theevent of temperature changes, the leakage between the two partstherefore remains largely the same.

The longitudinal bore 42 of the tappet 20 continues in the form of acoaxially extending continuous longitudinal bore 49 of the magnetarmature 19. A second pin 50 is received in the longitudinal bore 49.This pin, as shown in FIG. 1, is braced by one end toward the end wallon the valve dome 14. With its other end, the pin 50 engages the pin 46of the tappet 20 in a force-locking manner. The fit between the secondpin 50 and the longitudinal bore 49 of the magnet armature 19 can havegreater play than between the first pin 46 and the tappet 20.

In a departure from the exemplary embodiment, the magnet armature 19 andthe tappet 20 may also be penetrated by only a single pin.

The valve seat 28 of the valve body 25 and the closing member 37 of thetappet 20 form a seat valve 53, which assumes its open position in theabsence of a current through the magnet coil 16, because of the actionof the restoring spring 23. When current is applied to it, the valve 10can be switched into the closing position of the seat valve 53. Theelectromagnetically actuated valve 10 is thus a switching valve in theform of the 2/2-way valve. It can be used in hydraulic motor vehiclebrake systems, of the kind described at length in terms of circuitry andfunction in the German Patent Reference DE 41 19 662 A₁. When used insuch a way, the pressure medium inlet 26 of the valve 10 communicateswith a master cylinder, as a pressure generator of the brake system, andthe pressure medium outlet 33 communicates with a wheel brake, as apressure consumer.

Conventional switching valves are distinguished from the valve of theinvention for instance in that for the seat valve cone angles α greaterthan 90° are chosen, so that balls of larger diameter can be used as theclosing member 37, because such balls are easier to manipulate duringmounting on the tappet 20. Moreover, in the conventional seat valve, thegoal is to make the transition between the spherical face of the closingmember 37 and the tappet 20 free of sharp edges. Finally, in theconventional valve, the magnet circuit is designed such that themagnetic force rises increasingly more steeply at the transition to theclosing position.

The valve 10 of the invention is distinguished as follows over theconventional valves:

In the closing position of the seat valve 53, the inflow-side pressureP₁ acts on an operative area circumscribed by the sealing diameter D₂,which area is composed of a circular-annular face D₂ -D₁ of the tappetportion 38, this latter area being assigned to the closing member 37,and the end face, toward the valve seat, of the pin 46 in the tappet 20.The force exerted by the pressure P₁ on the pin 46 is diverted to thevalve dome 14 via the pin 50 of the magnet armature 19. Conversely, thepressure P₁ acting on the aforementioned circular-annular face D₂ -D₁exerts an opening force on the tappet 20. This force is comparativelyslight, because of the small size of the circular-annular face D₂ -D₁.The downstream pressure P₂ prevailing in the valve chamber 31 and in thevalve dome 14 acts on a circular-annular face D₂ -D₁ of the end facetoward the armature of the tappet 20 and generates a force acting in aclosing direction on the tappet. Since the pressure P₂ is lower than thepressure P₁, the hydraulic force Fxp resulting from these two forcesthus acts in the opening direction on the tappet 20. The prestressedrestoring spring 23, embodied as a helical compression spring, also actsin the opening direction on the tappet 20 with a force F_(F).

When the valve 53 opens from its closing position, the lower pressurelevel P₂ advances to a slight extent in the direction of the inflow bore29. However, since this bore is virtually equivalent to the sealingdiameter D₂ of the valve seat 28, and the circular-annular face D₂ -D₁has only a slight radial extent, no substantial reduction occurs in theopening force exerted by the pressure P₁ on the operative area of thetappet portion 38. On the condition of a constant pressure differencebetween P₁ and P₂, the resultant hydraulic force Fxp thereforedecreases, over the increasing valve opening stroke H only with aquantitatively slight negative slope, dropping monotonously. Since asexplained above the resultant hydraulic force Fxp can also assume onlycomparatively low values, this has substantial significance for thebalance of forces at the tappet 20 of the restoring spring 23. Becausethe restoring spring 23 has relatively high spring stiffness, the springforce F_(F) drops, as the valve opening stroke H increases monotonously,with a quantitatively great negative slope. Upon closure of the seatvalve 41, the conditions are reversed accordingly.

The course of the additively linked forces Fxp+F_(F) over the valveopening stroke H is shown in FIG. 3 in a graph in which the stroke H isassigned to the abscissa and the force F is assigned to the ordinate.The characteristic curve of this total force has a quantitativelyrelatively major negative slope. Since this depends essentially on thecharacteristics of the restoring spring 23 and depends less on thechange in hydraulic force Fxp over the valve opening stroke H, it isnecessary for the function of the valve 10 according to the invention toset the spring force very precisely. This can be done by displacing thesleeve 21 relative to the tappet, while the tappet portion 38 isengaging the valve seat 28, until the magnitude of the spring forcerequired for a zero stroke of the seat valve 41 is reached. Because ofthe press-fitted connection between the tappet 20 and the sleeve 21,this setting is made permanent.

The shaping of the seat valve 53 assures that the course of thecharacteristic curve Fxp+F_(F) given in the graph is largely free ofdisruptive influences. Thus by means of the relatively small cone angleα of the valve seat 28, an only slight deviation of the streams ofpressure medium in the seat valve 53 is attained. As a result, onlyslight pulsating forces, which occur especially at flow rates, arebrought about. The dependency of the valve properties on thedifferential pressure and on the temperature of the pressure medium istherefore slight. Moreover, because of the sharp-edged transitionbetween the closing member 37 and the tappet portion 38, it is assuredthat the flow of pressure medium will always separate there, thusleading to uniform flow forces on the closing member 37. Alsocontributing to a stable flow of pressure medium is the sharp-edgedtermination of the valve seat 28 at the end face 30 of the valve body25. The action of the pressure medium flow on the windings of therestoring spring 23 is therefore largely free of disruptive influences.Moreover, the axially recessed transitional portion 39 largely precludesstreams of pressure medium from striking the tappet 20.

The aforementioned hydraulic force Fxp and the spring force F_(F) aredirected counter to the magnetic force F_(M) generated by excitation ofthe magnet coil 16 and acting in the closing direction of the seat valve53. The magnetic force F_(M) must attain at least a magnitude such as tomove the seat valve 53 into the closing position, counter to therelatively slight hydraulic force Fxp and by comparison the high springforce F_(F), and keep it there. As the characteristic curve of themagnetic force F_(M) in the graph of FIG. 3 shows, it is attained byprovisions familiar to the persons skilled in the art in designing themagnetic circuit that for a certain exciter current I=constant, themagnet force F_(M) likewise assumes a monotonously decreasing courseover the valve opening stroke H, yet with a quantitatively lessernegative slope than that of the force course Fxp+F_(F). The shallowinclination of the characteristic curve F_(M) is attainable for instanceby suitable embodiment of the magnetic circuit, especially if in theclosing position of the valve 10 a relatively large remanent air gapbetween the magnet armature 19 and the pole core 13 remains, or if themagnet armature and the pole core are embodied as a plunging stage. Themagnetic force characteristic curve shown is representative for acertain exciter current I=constant. Characteristic curves that areshifted in the direction of the ordinate can be generated by means ofother exciter currents instead. Modified exciter currents can beestablished by means of current control, pulse-width modulation, andother known methods.

The two characteristic curves, Fxp+F_(F) on the one hand and F_(M) onthe other, intersect in the graph at a point where there is anequilibrium between the opening hydraulic force Fxp and the spring forceF_(F) on the one hand and the closing magnetic force F_(M) on the other.This point is designated as the operating point AP, at which the seatvalve 53 at the stroke h, assumes a stable position. If thecharacteristic magnetic force is shifted, by current control, in thedirection of the double arrow in the graph, the operating point is alonga different valve opening stroke. Therefore, despite its structuraldesign as a switching valve, the valve 10 of the invention can becontrolled, similarly to a proportional valve, in an infinitelygraduated manner as a function of current with a variable openingstroke. This controllability exists at least for short valve openingstrokes.

The valve 10 of the invention can be used in hydraulic motor vehiclebrake systems, for instance for brake slip or drive slip control or inbrake systems with a hydraulic servo pressure source for direct feedingof brake pressure into wheel brake cylinders. With the valve 10, aninfinitely graduated regulation of pressure and volumetric flow isadvantageously possible, if the brake system is equipped with suitablesensors and closed-loop control electronics. The valve 10 can also beused as a pressure limiting valve, by adjusting the response pressure,by means of current control, to either constant orapplications-dependent variable values.

The foregoing relates to a preferred exemplary embodiment of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed is:
 1. An electromagnetically actuated valve (10) forhydraulic brake systems of a motor vehicle, comprising the followingcharacteristics:a seat valve (53) provided between a pressure fluidinlet (26) and a pressure fluid outlet (33); the seat valve (53) has aclosing member (37) and a hollow-conical valve seat (28), into which aninflow bore (29), communicating with the pressure fluid inlet (26),discharges centrally with a diameter (D₁) corresponding substantially toa sealing diameter (D₂) of the valve seat; the closing member (37) isprovided with a sharp-edged transition to the face end of a tappet (20);the tappet (20) is engaged by a magnet armature (19) acting closingly onthe seat valve (53) and at least indirectly by a restoring spring (23)acting in an opening direction; a closing force (F_(F)) at the closingmember (37), originating in the restoring spring (23), is adapted suchthat the closing force has a course that decreases monotonously with anincreasing valve opening stroke (h); a magnet circuit of the valve (10)is formed such that a magnetic force (F_(M)) exerted on the magnetarmature (19) and transmitted to the closing member (37) is variable ininfinitely graduated fashion and has a course that decreasesmonotonously with an increasing valve opening stroke (h), the magnetarmature (19) is disposed in a valve dome (14) that communicates apressure medium with the pressure outlet (33); the tappet (20) has alongitudinal bore (42), which begins at the closing member (37) and inwhich a longitudinally movable pin (46) supported at least indirectly ona wall of the valve dome (14) is received, a cross section of the pincorresponding at least approximately to a cross section of the inflowbore (29), a cone angle (α) of the valve seat (28) is at most 90°; theclosing member (37) has the form of a spherical layer; and the course ofthe magnetic force (F_(M)) over the valve opening stroke (h) has anegative slope, which is quantitatively less than that of the course ofthe spring force.
 2. The valve of claim 1, in which the closing member(37) is included on a tappet portion (38) whose diameter (D₃) isapproximately equivalent to the sealing diameter (D₂) of the valve seat(28).
 3. The valve of claim 1, characterized in that the valve seat (28)terminates freely with a diameter (D₄) that is at least twice thesealing diameter (D₂) of the valve seat.
 4. The valve of claim 2,characterized in that the tappet portion (38), after a length (L)corresponding to at least the sealing diameter (D2) of the valve seat(28), ends at a transitional portion (39) whose conicity corresponds tothat of the valve seat.
 5. The valve of claim 1, in which the tappet(20) has a sleeve (21) press-fitted onto the tappet (20) that has asupport face (24) for the restoring spring (23).